What that tells me is that the error must be in a template rather than a source file (since only templates are executed via eval from Load.php), and after that it's going to be a very short list of places to look depending on what action you were calling.

So knowing what the logged URL was is about as important (or at least, what the user was doing when the error occurred, either way works), since each action or subaction will load a given subtemplate. Odds are it's possible to figure that out while waiting for the user to go through and figure out how to disable template eval.